Pulse-Driven Active-Site Switching on Bromine-Modified Cu Enables Sequential 2e – + 6e – Nitrate-to-Ammonia Conversion

Steady active-site electronic states commonly lead to product decentralization and energy consumption increase when overcoming the kinetic mismatch within 8-electron transfer inherent in the electrocatalytic nitrate reduction reaction (NO 3 RR) to NH 3 . Here, we first report a reversible and self-adaptive regulation of Cu active sites by Br modification in pulsed electroreduction electrolysis (PE) to match distinct reaction kinetics steps of the (2 + 6)-electron pathway for the NO 3 RR on trace-Br-modified Cu/Cu 2 O catalysts (Br–Cu). Mechanistic investigations integrating in situ spectroscopy and DFT calculations reveal that Br-mediated electronic modulation and d -band center downshift strengthen Cu active sites to possess a reversibly tunable Cu δ+ (0 < δ < 1) state under PE, which selectively favor the first 2-electron (*NO 3 → *NO 2, δ close to 1) and the latter 6-electron (*NO 2 → *NH 3, δ close to 0) steps, delivering 94% Faradaic efficiency. The continuous-flow electrochemical cell employing Br–Cu maintains high NO 3 – conversion, NH 3 Faradaic efficiency, and NH 3 selectivity in approximately 700-h electrolysis while enabling efficient NH 3 recovery from real aquaculture tailwater. This work presents a robust strategy for programmable self-adaptive electronic modulation toward sustainable NH 3 electrosynthesis.